Microsoft has launched the campaign for the most dramatic changes to its Windows operating system in years, with Windows 8 designed to run on both PCs and the increasingly popular tablet computers.
"We kicked off a new era for Microsoft and a new era for our customers," Ballmer said.
Windows 8 attempts to bridge the gap between personal computers and tablets with its touch-enabled interface. Another version of Windows 8 is being released for smartphones next week.
Windows 8 represents a big risk for Microsoft because it looks and operates so much differently than previous versions.
The redesign discards the familiar "start" button and menu that Windows has had since 1995 when users are operating in a desktop mode, a change that critics believe will almost certainly provoke howls of protest. But many reviewers applaud Microsoft for overhauling Windows so it greets users with a mosaic of tiles displaying applications instead of relying on the desktop icons that served as the welcome mat for years.
The redesign could frustrate many long-time users and cause them to consider checking out computers made by Apple Inc., which has been gaining market share in the past few years.
Microsoft's decision to sell a Windows 8 tablet also threatens to alienate the device makers who license Windows 8 for their desktop PCs, notebook computers and tablets.
It's a gamble that Microsoft felt it had to take because people are increasingly embracing smartphones and tablets such as Apple's hot-selling iPad to take care of their computing needs. The shift has contributed to decline in PC sales, hurting Microsoft and the makers of desktop and laptop machines, including Hewlett-Packard and Dell.
Microsoft shares dipped 4 cents to $US27.87 in early afternoon trading.
The launch event comes amid other tablet offerings ahead of the holidays. Apple unveiled its iPad Mini with a 7.9-inch (20-centimetre) screen on Tuesday. Amazon.com and Barnes & Noble, makers of the 7-inch (17.7-cm) Kindle Fire and Nook Tablet, are coming out with larger versions next month.
The Windows event also heralded the launch of the software company's Surface tablet, its first venture into making computer devices. The device goes on sale tomorrow, as will computers and other tablets running Windows 8.
Wedge Partners analyst Kirk Adams expects Microsoft to trail its rivals in fourth-quarter tablet sales.
One factor that might dampen enthusiasm for the Surface is its price - $US599 with its touch keyboard cover and its availability for purchase only from a limited number of Microsoft stores and online, Adams said. He said consumers may be reluctant to buy the device until they can try it in person.
Meanwhile, most analysts believe companies and governments will hold off on upgrading to Windows 8 for at least another year. About half of business users still haven't upgraded to Windows 7 from Windows XP, which came out in 2001.
-AP
